1. Field of the Invention
This invention pertains generally to a combination catalytic process for producing alcohols directly from synthesis gas (syngas) or any gas containing carbon monoxide and hydrogen. More particularly, the present invention pertains to a multi step catalytic process that promotes specific hydrogenation and homologation activities to improve the selectivity and yield of ethanol from a stream of syngas.
2. Description of Related Art
Global demand for energy continues to rise at a significant rate, particularly among developing industrialized nations. The increasing dependence of the United States on foreign sources of oil and natural gas and diminishing reserves have led energy producers to consider alternative or less conventional sources of energy for electricity production, domestic heating and transportation.
One source of energy that is available as an alternative to foreign sources of natural gas and petroleum in the United States is domestic coal. Coal continues to be an important source of fuel for electricity generation as well as a feedstock for chemical production. However, using coal as a primary source of fuel requires extensive processing to alleviate dust and gas emissions and other environmental concerns.
Converting coal into gas and other materials can also provide greater energy conversion efficiencies than found with traditional combustion in existing coal-fired power plants. Environmental pollutants may also be reduced over pulverized coal electricity production with the use of gasified coal.
The typical gasification process consists of placing coal in a vessel under high temperature and pressure and then introducing steam and oxygen into the vessel. The organic materials that are present in the coal are converted into carbon monoxide, carbon dioxide, hydrogen, and other carbon compounds. Other gases present include methane, and small amounts of ethane and propane. The combustible hydrogen and carbon monoxide components are typically separated from non-combustible water vapor, carbon dioxide and other gases. This mixture of combustible gasses from gasified coal is often referred to as synthesis gas or “syngas.” Syngas may be used for combustion or as a feedstock for gas-to-liquid processes such as the Fischer-Tropsch process that produces valuable organic materials such as distillate fuels, naphtha and wax.
The high price of natural gas and oil has also caused the chemical industry in the United States to examine alternative feedstocks for the production of marketable chemicals. The chemical industry is the largest consumer of natural gas in the country and the substantial coal reserves make coal byproducts an attractive alternative to natural gas. Historically, coal gasification research has primarily focused on energy fuels and power production, with less emphasis on chemical production. For example, ethanol has been used as a fuel and as petroleum fuel additive that has the potential of reducing consumption and dependence on foreign oil. Adding ethanol to gasoline “oxygenates” the fuel mixture so that it burns more completely and reduces polluting emissions such as carbon monoxide. Brazilian domestic fuel, for example, currently contains at least 24% ethanol typically produced from sugar cane.
However, ethanol may also be used as a feedstock for the production of commodity chemicals. At the present time, much of ethanol that is not intended for human consumption is made synthetically, either from acetaldehyde made from acetylene, or from ethylene made from petroleum. Ethanol can also be oxidized to form acetaldehyde and then acetic acid and can be dehydrated to form ether. Ethanol is useful as a solvent for many substances and as a feedstock for many other organic compounds used in making perfumes, paints, lacquer, and explosives. For example, butadiene can be derived from ethanol that may be used in making synthetic rubber.
The technology for the production of syngas from various sources is well developed and advancements in production efficiency continue. Other sources of synthesis gas such as pyrolysis of wood and other agricultural waste and organic land fill waste are also under development. Unfortunately, present processes for the production of ethanol directly from syngas or any gas containing carbon monoxide and hydrogen do not have high selectivity for ethanol and are very complicated, inefficient and expensive processes.
Accordingly, there is an increasing need for a process that can directly convert syngas to ethanol with a high yield at relatively low cost. The present invention meets these needs as well as others and is a substantial improvement over the art.